Method for measuring level of large structure

ABSTRACT

Displacement sensors which are communicated with a stationary reference side are placed at the measuring points of a large structure. Displacement at each measuring point is electrically measured by utilizing the fact that the liquid levels at the stationary reference side and each measuring point are at the same level.

This application is a continuation of application Ser. No. 07/068,522,filed July 1, 1987 and now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method for measuring the level of alarge structure such as a bridge.

In recent construction or reconstruction of a large bridge or the like,the latter is composed of block assemblies and is assembled in such amanner that every time when each block is mounted, displacement of thethus partially constructed large structure is measured.

In construction of a bridge or the like, major sections or blocks maydeflect partially or over the whole length thereof due to environmentalconditions such as variation of loads. Especially in recent constructionof a large bridge or the like, the span between upright bridge pierserected from the ground surface or the bottom of a river is considerableso that when individual blocks are interconnected into a unitaryconstruction, it becomes one of technical factors in the construction toestimate the local or overall deflection of a large structure fromdetected deflections of the major structural blocks or from detectedvariations in level at specific points. Measurement of such deflectionsin construction of a bridge as long as, say, 1km or more, which isgenerally carried out during the night, will take a long period of timeand many measurement steps so that the measurement and the processing ofthe measured data become very cumbersome.

A simple method for measuring deflections of a bridge or the likedescribed above is a so-called water leveling method which has beenwidely used.

FIG. 1 is a view used to explain the general principle of the waterleveling method. Measuring pipes b and c are connected to respectiveends of a length of tube a. The measuring tube b is installed on asupporting stand g which is disposed at a measuring point e and has ameasurement indication line f above the measuring point e while theother measuring tube c is so disposed as to be movable along a scale jinstalled at a reference measuring point i on the stationary side h (theground or a main pier) with known altitude.

For measurement, operators are assigned to the measuring point e andreference measuring point i, respectively, and the measuring tube c atthe reference measuring point i is moved upwardly or downwardly so thatthe liquid level in the measuring tube b at the measuring point e maycoincide with the measurement indication line f. When the liquid levelcoincides with the measurement indication line f, the operator reads outthe height of the liquid level in the measuring tube c from the scale j.

Thereafter the measurement is repeated in a manner substantially similarto that described above to read out a graduation. When the graduationthus measured is found to be different from the graduation obtained inthe first measurement, you will know that the point e on the bridge d isdisplaced upwardly or downwardly by a height equal to the differencebetween the graduations read out in the first and second measurements.

In measurement of displacement of a bridge or the like, levelingmeasurements on the sides of the bridge and at a position on a centerline thereof are repeated every a few to 30 meters (as needs demand) inthe longitudinal direction of the bridge so that every time when themeasurement is made, the operator moves the measuring tube b and thesupporting stand g to the next measurement point.

In the above-mentioned method, two operators are required on the side ofthe measurement point e and the reference point i, respectively, and afurther operator is needed to record the measurement data. Thus, thismethod needs the operators and a long period of measurement time. Inaddition, such measurements as described above are generally carried outnear midnight in order to eliminate displacements caused by the solarenergy during the daytime so that the measurement efficiency is verylow. In addition, because reading of the coincidence of the liquid levelin the measuring tube b with the measurement indication line f and thereading of the scale j are visually made by the operators so that notonly measurement errors but also failure in recording the measurementdata tend to occur from time to time. Furthermore, since the measurementis carried out during the night, an illumination system must be used sothat the measurement operation becomes harder. Moreover, from thestandpoint of operation efficiency and reliability of the measurementdata, there arises the problem that the communication between theoperators in order to confirm the coincidence of the liquid level in themeasuring tube b with the measurement indication line f becomesdifficult when the distance between the measurement point e and thereference point i is increased.

The present invention was made to overcome the above and other problemsencountered in the conventional water level measurement methods and hasfor its object to provide a method for measuring displacements atvarious points on a large structure such as a bridge in an efficientmanner within a short period of time with a high degree of accuracy byutilizing the water leveling method.

The above and other objects, effects and features of the presentinvention will become more apparent from the following description ofpreferred embodiments thereof taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view used to explain a conventional water levelingmethod;

FIG. 2 is a view used to explain a first embodiment of the presentinvention;

FIG. 3 is a detailed view used to explain displacement sensor means;

FIG. 4 is a view used to explain a vessel in which a liquid level iskept constant by utilizing an overflow mode;

FIG. 5 is a view used to explain a second embodiment of the presentinvention incorporating a lift; and

FIG. 6 is a view used to explain another displacement sensor means andlift.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Briefly stated, according to the present invention, displacement sensormeans comprising a float floating at the liquid level of a liquid tube,a movable indicator movable upwardly or downwardly in unison with saidfloat j and a sensor supported on a stationary member for detecting thedisplacement of said displacement indicator is disposed at a measurementpoint of a large sturcture whose level is to be detected. The lower endof the liquid tube is communicated through a liquid distribution linewith a vessel which is disposed on a reference stationary side which isnot vertically movable so that the level of the measurement point iselectrically measured by utilizing the fact that the liquid level insaid vessel and the liquid level in the liquid tube disposed at themeasuring point are always at the same level.

Furthermore, according to the present invention, the measurement mode isswitched between the case in which the levels at a plurality ofmeasurement points on a large structure are substantially the same andthe displacements of levels are relatively small and the case in whichit is expected that the levels of a plurality of measurement points areconsiderably different from the initial states or the displacements aregreat, so that the measurement process becomes very efficient and themeasuring system can be simplified.

FIG. 2 shows a first embodiment of the present invention used when thelevels at a plurality of measurement points are substantially the sameand the displacements of levels are relatively small. A tank 4containing a body of measuring liquid 3 is disposed on a stand 2 whichin turn is disposed on a reference stationary side 1. Referenceliquid-level sensor means 5 is mounted on the tank 4.

A liquid distribution line 6 is communicated with the tank 4 and aplurality of displacement sensor means 8 are disposed in parallel witheach other and communicated with the liquid distribution line 6 throughupright lines 7, respectively. The displacement sensor means 8 aresecurely mounted on structural components 9 such as handrails, girdersand beams of a bridge 25 with mounting members 10 such as mountingfixtures, bands or the like and are spaced apart from each other by apredetermined distance. In FIG. 2, reference numeral 11 represents aliquid supply line for supplying the measuring liquid into the tank 4;and 12 designates valves.

FIG. 3 shows one example of displacement sensor means 8. Thedisplacement sensor means 8 comprises a liquid tube 13 whose lower endis communicated with the upright line 7, a probe 15 whose upper endportion is securely joined to an upper end cap 14 of the liquid tube 13and whose lower end portion extends by a predetermined length coaxiallyof the liquid tube 13, a float 16 vertically movable along the probe 15within the liquid tube 13, and a detector amplifier 18 for generating asignal representative of the position of a position sensing magnetichead (displacement indicator) 17 incorporated in the float 16. In FIG.3, reference numeral 19 designates a ring securely joined to the liquidtube 13 so that the probe 15 can be maintained coaxially of the liquidtube 13 with a predetermined allowance. The ring 19 is formed with asuitable number of holes for permitting the flow of the measuring liquidtherethrough. Reference numeral 20 denotes an opening formed at theupper portion of the liquid tube 13.

The reference liquid-level sensor means 5 comprises a probe 15 extendingin the body of the measuring liquid 3 and securely joined to the tank 4,a float 16 vertically movable along the probe 15, a magnetic head 17 anda detector amplifier 18.

Detection signals from the detector amplifiers 18 of the sensor means 5and 8 are transmitted through a signal cable 21 to a scanner 22 disposedon the side of the reference stationary side 1 and then to a measurementinstrument 23 adapted to store the transmitted detection signals and tocarry out arithmetic operations of them so that the displacements aredisplayed and recorded. Furthermore, there is a recorder 24 forsuccessively recording (and concurrently displaying) the signalstransmitted from the sensor means 5 and 8.

The sensor means 8 are respectively installed at a measuring point onthe bridge 25; the height of the sensor means 8 is so adjusted that theliquid level L (that is, the position of the float) is maintained at themid-point of the effective detection length H (that is, the allowabledisplacement length of the float) of the displacement sensor means 8 orat a suitable level within the effective detection length H when thevertical displacement of the liquid is expected. Thereafter thedisplacement sensor means 8 is securely attached to the structuralcomponent 9 with the mounting fixture 10 (as shown in FIG. 2).

With this arrangement, the tank 4 is communicated with the liquid tubes13 in the displacement sensor means 8 through the liquid distributionline 6 and the upright lines 7 so that the displacement sensor means 5and 8 have the same liquid level L and consequently the floats arelocated at the same height.

Under these conditions, the detection signals from the sensor means 5and 8 are sequentially switched and applied to the measuring instrument23 so that the position of the magnetic head 17 in the float 16 relativeto the probe 15 is stored and recorded.

In the case of the measurement of the displacement of the bridge 25during or after construction of the same, the detection signals from thesensor means 5 and 8 are applied through the scanner 22 to the measuringinstrument 23 and are compared with the previously stored detectionsignals and the differences are recorded.

When the measuring point on the bridge 25 is vertically displaced, theliquid tube 13 securely joined to the structural component 9 isdisplaced simultaneously. However, the liquid level L is not varied sothat the position of the float 16 relative to the probe 15 varies andthis displacement is read out by the measuring instrument 23 as adisplacement of the measuring point.

When the quantity of liquid within the tank 4 varies during theabove-mentioned measurement process, the liquid level L varies; but asdescribed above, the level L within the tank 4 has been detected by thereference liquid-level sensor means 5 and then stored so that in thenext measurement, the displacement of the liquid level L can bedetected. Therefore it becomes possible to detect a correct displacementby adding or subtracting the displacement to and from the detecteddisplacement at each measuring point. When the area of the free surfaceof the liquid in the tank 4 is by far greater than the sum of the areasof the free surfaces of the liquid in the displacement sensor means 8and when the displacement of the liquid level in the tank 4 in responseto the variation in liquid level in the sensor means 8 is small andtherefore is negligible, the reference liquid-level sensor means 5 maybe eliminated.

In the first embodiment, a vibrator V may be mounted on the tank 4 so asto vibrate the body of measuring liquid 3, whereby any difference inliquid level between the tank 4 on the one hand and the displacementsensor means 8 on the other hand are eliminated; upward floating andvanishing of any air bubbles produced are facilitated; and response timerequired for stabilization of the variation in liquid level due to thevertical movement of the displacement sensor means 8 is accelerated sothat correct measurement is ensured.

According to the above-mentioned method, displacements occurring at tensor hundreds of measuring points can be measured within a few secondswith an extremely high degree of accuracy.

As shown in FIG. 4, a liquid-receiving tank 26 may be formed around theouter cylindrical surface of the tank 4 which is communicated with theliquid distribution line 6. The measuring liquid 3 in theliquid-receiving tank 26 is returned into the tank 4 through a pump 27so that during the measurement the liquid in the tank 4 is permitted tooverflow and consequently the liquid level L can be maintained constant.Reference numeral 28 designates an overflow sensor for detecting whetheror not the measuring liquid is overflowing.

With this arrangement, the liquid level L can be maintained at apredetermined level and will not vary so that any reference liquid levelmeasuring instrument on the tank 4 can be eliminated and thedisplacements can be obtained merely by reading the positions of thefloats 16 of respective displacement sensor means 8 and comparing themwith the stored data.

In the above-mentioned embodiments, the present invention has beendescribed in connection with the case in which the levels at a pluralityof measuring points are almost the same; but it is to be understood thatwhen a plurality of displacement sensors which are disposed at aplurality of measuring points at which the levels are almost the sameare read out as a block, a great many measuring points at which thelevels are considerably different from each other can simultaneously bemeasured.

FIG. 5 shows another embodiment of the present invention applied to thelevel measurement when the levels or displacements of a plurality ofmeasuring points are expected to be considerably different from eachother in the vertical direction. A plurality of displacement sensormeans 8 are disposed at a plurality of measuring points on a bridge 25where the levels are greatly different from each other (as indicated byS). Furthermore, liftable sensor means 8' which is substantially similarin construction to the displacement sensor means 8 and which can bevertically moved by a lift 29 is disposed on the reference stationaryside 1. The liquid tubes 13 and 13' of the sensor means 8 and 8' areintercommunicated with each other through the liquid distribution lines6 and a switching unit or means 30.

The sensor means 8 and 8' are connected through the detector amplifiers18 and 18' and signal cables 21 to a control unit 31. The detectionsignal from the sensor means 8' is also applied to the measuringinstrument 23.

The detection signal from a vertical position sensor 32 such as a rotaryencoder adapted for detecting a vertically displaced position of thesensor means 8' by the lift 29 is applied to the control unit 31. Inresponse to a switching signal 33 delivered from the control unit 31,switching valves 34, make-up feed valve 34' and a drain valve 34" withinthe switching unit 30 are opened or closed; and in response to the drivesignal 35, a drive motor 36 in the lift 29 is energized. Thus the valves34, 34' and 34" and the drive motor 36 are automatically controlled. InFIG. 5, reference numeral 37 designates a liquid supply tank; and 38, adrain pipe.

In level measurement, after the liquid is supplied and all the valves 34are closed, the drive motor 36 is energized so that the height of thesensor means 8' above the reference stationary side may becomesubstantially equal to the height of one of the displacement sensormeans 8. Thereafter the selected sensor means 8 and the liftable sensormeans 8' are intercommunicated through the liquid distribution line 6 byopening the corresponding valve 34. Next the drive motor 36 is energizedto vertically move the liftable sensor means 8' on the side of thereference stationary structure 1 in such a way that the liquid level inthe liquid tube 13 at the measuring point coincides with the measurementlevel (for instance, the point 0 at which the mid-point in the verticaldirection of the magnetic head 17 coincides with the mid-point in thevertical direction of the probe 15). That is, the operation is carriedout for always maintaining the distance between the measuring point onthe bridge 25 and the liquid level in the liquid tube 13 of thedisplacement sensor means 8 at a predetermined distance. In this case,because the detection signal from the sensor means 8' is applied to thecontrol unit 31, the drive motor 36 may be controlled in response to thedigital display of the detection signal or the above-mentioned 0-pointadjustment may be carried out automatically by operating buttons on thecontrol unit 31.

The liquid levels in the liquid tubes 13 and 13' are always at the samelevel so that when the measurement level is attained, the height of theliquid tube 13' is read out by the rotary encoder 32 and the liquidlevel in the liftable sensor means 8' is read out by the position of thefloat 16' in the liquid tube 13' relative to the probe 15'. Themeasurement results are stored in the measuring instrument 23.

After a predetermined time interval and after the completion of arequired operation, the measurement is repeated in the same manner andwhen the measurement result is different from the stored result of thepreceding measurement, any difference between them is determined as thedisplacement at the measuring point and is displayed by the measuringinstrument. The detection data thus obtained may be outputted by aprinter or the like (not shown) connected to the measuring instrument23.

In the case of the level measurement at a plurality of measuring pointsby a plurality of displacement sensor means 8 each disposed at ameasuring point, and in which only the valve 34, inserted in the liquiddistribution line 6 communicated with the liquid tube 13 which measuresthe level is opened in response to the switching signal 33 deliveredfrom the control unit 31 by operating the buttons thereon themeasurement is sequentially repeated so that the efficient switching canbe ensured and the level at each measuring point can be measuredsuccessively.

FIG. 6 shows another construction of the displacement sensor means aswell as another construction of the lift. The displacement sensor means8 has therein a float 16 as well as a displacement indicator 40 such asan iron core which is vertically movable in unison with the verticalmovement of the float 16 within a small-diameter tube 39' which in turnextends upwardly from the upper end of the liquid tube 39 and iscommunicated with the surrounding atmosphere.

A lead-screw 44 which is rotated through a reduction gear 43 by a drivemotor 42 is vertically supported by a detection column 41 and passesthrough a threaded nut 45 in such a way that upon rotation of thelead-screw 44, the nut 45 is displaced upwardly or downwardly. Theliquid tube 39 is securely joined to the nut 45 through a mountingfixture 10, whereby the lift 29 is provided. A sensor 46 is attached tothe upper end portion of the column 41 in such a way that it surroundsthe small-diameter tube 39' extending upwardly from the upper end of theliquid tube 39 in order to detect a vertical position of thedisplacement indicator 40 without contact with the liquid level byutilizing an electric method using a differential transformer, a methodusing a high-frequency detector or a method using ultrasonic waves or alaser beam. The detection output signal from the sensor 46 istransmitted through a signal cable 21 to the measurement instrument 23mounted on the stand.

According to the level measurement method of the present invention, themeasurement is immediately made when required regardless of whether itis day or night and the resultant measurement data can be compared withthe previous measurement data so that the displacement at each measuringpoint can be obtained. Furthermore, as described above, in the levelmeasurement, a suitable measurement method may be selected dependingupon the level, displacement and so on of a large structure so that theefficient and stable measurement can be ensured.

The present invention is not limited to the above-described embodiments,but various modifications may be made without leaving the scope of thepresent invention. For instance, the present invention may be equallyapplied to the measurement of displacements at a great many points onviaducts for railway or highway traffic, roads, marine and portinstallations in addition to bridges. Instead of detecting the positionof the float by the probe, other suitable detection methods utilizinghigh frequency waves or ultrasonic waves or optical methods utilizing alaser beam or the like may be used to ensure the measurement with a highdegree of accuracy. The measuring liquid may be water, an anti-freezingagent, oils and so on. The number of measuring points is not limited.The vertical position of the vessel itself may be varied.

As described above, according to the level measurement method of thepresent invention, the displacement sensors which are communicatedthrough the liquid distribution line or lines with the referencestationary side are placed at the measuring points; the liquid level ineach displacement sensor is detected by an electrical method or anyother suitable methods; the detected result is stored and compared withthe result of the succeeding detection to measure the displacement ateach measuring point so that the measurement operation can beautomatically and efficiently carried out during daytime or at night andthe number of required operators can be reduced. Furthermore, themeasurement with a high degree of accuracy is ensured and calculations,storage and display can be made by the measuring instrument so that themeasurement operation can be considerably facilitated.

What is claimed is:
 1. A method of measuring vertical displacement of alarge structure relative to a stationary reference point, comprising thesteps of: placing at the stationary reference point a vessel having anupper portion open to atmosphere; disposing reference liquid-levelsensor means in said vessel; said reference liquid-level sensor meanscomprising a liquid-level sensor body vertically secured in said vessel,a float around an outer periphery of the sensor body and verticallymovable with the level of a liquid in said vessel, and a displacementindicator vertically movable in unison with said float; placing aplurality of liquid tubes respectively at a plurality of measuringpoints of said large structure and substantially at the same level assaid vessel, each of said liquid tubes having an upper portion open toatmosphere and communicating with said vessel through liquiddistribution line means; disposing displacement sensor means in each ofsaid liquid tubes; said displacement sensor means comprising aliquid-level sensor body secured centrally in the respective liquidtube, a float around an outer periphery of the last-mentioned sensorbody and vertically movable with the liquid level in the respectiveliquid tube, and a displacement indicator movable in unison with saidlast-mentioned float; effecting electrical detection of the liquid levelby said reference liquid-level sensor means and said displacement sensormeans; generating a measuring point liquid level initial output signalfor each measuring point using the displacement sensor means at eachmeasuring point, generating a reference liquid level initial outputsignal for said reference point using the reference liquid-level sensormeans at the reference point; storing the initial output signal fromsaid reference liquid-level sensor means and the initial output signalsfrom said displacement sensor means in a storing means; and thereafterre-effecting electrical detection of the liquid level using saidliquid-level sensor means and said displacement sensor means liquidtubes and generating further measuring point liquid level output signalsfor each measuring point, and detecting displacements at the measuringpoints by comparison of the further measuring point liquid level signalsto the initial measuring point liquid level output signals stored insaid storing means and correcting for any variation of the referencepoint liquid level by re-effecting electrical detection of the referencepoint liquid level using the reference point liquid-level sensor means,generating a further reference point liquid level output signal,comparing the further reference point liquid level output signal to theinitial reference point liquid level output signal stored in the storingmeans, defining a correction factor which corresponds to the differencebetween the further reference point liquid level output signal and theinitial reference point liquid level output signal, and applying thecorrection factor to the further measuring point liquid level outputsignals.